1. Field of the Invention
The present invention is related to pressure responsive holding devices. More particularly, the present invention pertains to pressure compensation apparatus for responding to fluid pressures, tending to dislodge a first element from engagement with a second element, whereby gripping means are actuated to anchor the first element relative to the second with force which increases as the pressure increases. Such pressure compensation apparatus find application in well tools where downhole fluid pressures tend to dislodge tool elements from a desired configuration.
2. Description of Prior Art
Well packers are used for a variety of purposes to seal one or more tubing strings, or other tubular bodies to a surrounding casing, or conduit, within a well. Generally, such a packer is positioned within the conduit, then set by manipulating the packer to expand sealing members, carried by the packer, into sealing engagement between the packer body and the conduit. Anchoring means, such as slips, are also made to engage the conduit in the set packer configuration to anchor the packer in place relative to the conduit, thereby preventing the sealing engagement of the sealing members with the conduit from being disturbed.
U.S. Pat. Nos. 3,279,542; 3,357,489; 3,467,184; and 3,659,647 as well as copending U.S. patent application Ser. No. 612,226, filed Sept. 10, 1975, now U.S. Pat. No. 4,018,274, issued Apr. 19, 1977 show setting and anchoring mechanisms which anchor the packer body to the well conduit with slips subject to wedging action from both vertical directions. Such dual wedging is advantageous for preventing fluid pressure in the well from unsetting the packer from either direction. An improvement in the setting of a weight set packer is disclosed in copending U.S. patent application Ser. No. 750,801, filed Dec. 15, 1976, assigned in part to the assignee of the present application, wherein the initialy set packer may be tightened in its set configuration. Such a feature provides the advantage of increased forces holding the packer in anchoring and sealing engagement with the surrounding conduit.
In the aforementioned patents and patent applications, with the exception of U.S. Pat. No. 3,659,647, a bypass passage is provided through the packer in addition to the primary flow passage provided within the tubing string which is extended through the packer. The bypass passage may be opened or closed by raising or lowering the tubing string to selectively permit or prevent fluid flow by the set packer along the annular region between the tubing string and the well conduit. While the aforementioned anchoring means are intended to hold the set packer body in place against the urging of well fluid pressure, the tubing string is subject to the same pressures, and adequate provision must be made to selectively maintain the tubing string in place to keep the bypass passage closed. To this end, pressure compensating devices may be provided for responding to pressure differentials across the set packer tending to move the tubing string longitudinally to open the bypass passage. The compensating devices thus react by increasing forces tending to hold the tubing string in place as the pressure differentials increase. An annular piston and split ring are used in U.S. patent application Ser. No. 612,226, filed Sept. 10, 1975, now U.S. Pat. No. 4,018,274, issued Apr. 19, 1 while a split locking ring and piston are shown in the second aforementioned copending U.S. patent application Ser. No. 750,801, filed Dec. 15, 1976. There, beveled surfaes of the locking ring and the annular piston cooperate to produce radially inward force components keeping the locking ring, held by the set packer body, in threaded engagement with a mandrel assembly attached to the tubing string to prevent longitudinal movement of the tubing string.